How to shield a live wire at 240V ?

[_q12x_]

I have a electronic board with leds (made by me) that is driving a relay. When that relay is closing it’s contacts, is actually switching the 240V for the light bulb switch in my room. This board is quite long, like 50cm (half a meter). The relay is in the left corner, and the live wires from it goes in behind the board to the hole in the wall for the mains switch. I also have a mild steel sheet behind my board that is grounded. It is shielding the interference of the 50Hz from the live wires from the wall to my sensitive circuit. But even If I have this grounded metal shield behind my board, the live wires from the relay are still affecting my entire circuit board, keeping it ON all the time. If I am disconecting the live wires from the relay, the board is functioning very well. Another IF, is if I disconnect the ground from the metal shield, the circuit board goes nuts. So the shield is doing it's job fine, but only for the live wires inside the wall !!! But not for the wires from the relay to the live switch.
- I want a way to shield these wires !
Thank you !

 

[marconi]

I have ordered some 940nm ir LEDs and photodiodes to make some longer wavelength arrays. So far they have been 850nm ones.

I found this scientific paper to learn more about how human skin reflects and absorbs ir rays. Do not worry about the mathematics just read the words if you are interested.

https://www.osapublishing.org/Direc...4-35-10559.pdf?da=1&id=333549&seq=0&mobile=no

 

[_q12x_]

I have ordered some 940nm ir LEDs and photodiodes to make some longer wavelength arrays. So far they have been 850nm ones.

I found this scientific paper to learn more about how human skin reflects and absorbs ir rays. Do not worry about the mathematics just read the words if you are interested.

https://www.osapublishing.org/Direc...4-35-10559.pdf?da=1&id=333549&seq=0&mobile=no

your link is giving me an error:

Always check the links you send ,if they first work in your side.

 

[marconi]

These are the items my links should have shown you.

My ir sensor has the predictable problem of variable ambient ir radiation pick up. Worse of course during the day. One of the reasons for trying 950nm ir is it less reflective off skin which may reduce pick up of ambient ir reflected off it and thereby emphasise the ir from the led illuminators. We will see.

I also thought I could pulse the illuminators which would create pulsed reflections I can build a circuit to distinguish from the ambient ones. As ever work in progress and most interesting.

I bought a sounder too to tick.

 

[_q12x_]

I was waiting for you to send me back that link that didn't work. When you send the link, make a test if its working in your side, immediately after you send the message. Then you can press the "edit" to change the link if is still not working.
Officially they are called buzzers and not sounders. Is a keyword that works in google and on ebay or any other online market. I am using the correct one because I learned to respect these keywords over the years and they just work. So get in habit to use them correctly as well. Its how I do things and it helped me.
I already find the solution for IR problem. You need much more bigger wattage IR leds to be able to reflect from your skin or any other opaque material. Just try it my way and we (both) will see if is true or not. I didnt test it but I think it might work. THese little 5mm are good if the receiver and emiter leds are pointing at each other, and not reflected like you are trying there.

 

[_q12x_]

I made a "quick" (10min) movie describing and showing the problem with Rx Data pin (its output).

 

[marconi]

I will take a look later but more likely tomorrow morning when I get up.

Could you clarify something for me please? Have you actually done a 1W IR led shining on your hand and then reflected back to a photodiode? I know you did a beam interrupter system using visible light LED and PD. If you did how did you arrange the IR led and photodiode at one place? Also please tell me what wavelength you used. Such experience would save me some effort and time.

Regards M

 

[_q12x_]

I will take a look later but more likely tomorrow morning when I get up.

Could you clarify something for me please? Have you actually done a 1W IR led shining on your hand and then reflected back to a photodiode? I know you did a beam interrupter system using visible light LED and PD. If you did how did you arrange the IR led and photodiode at one place? Also please tell me what wavelength use used. Such experience would save me some effort and time.

Regards M

It was a theory I had some couple of reply ago. But you didnt read all I wrote before. I did not made any attempt before. It just crossed my mind (while discussing it with you here in forum) to use 1W IR led and also there are 100W IR leds as well and it is a good idea to try it.

 

[marconi]

It was a theory I had some couple of reply ago. But you didnt read all I wrote before. I did not made any attempt before. It just crossed my mind (while discussing it with you here in forum) to use 1W IR led and also there are 100W IR leds as well and it is a good idea to try it.

How do you know I did not? In your #244 you wrote 'I already find the solution for IR problem.' You have not then found the solution: you have an idea on what the solution might be.

 

[marconi]

[Remote Control Transmitter and Batteries Built in one day]
Here is 1 day of very hard work and very good results.
I apologize for a very long movie 21min.
But you will see in it how it behaves on the breadboard and how is in my hand. Also some photos of how was built, and also my "3d printing" method I used. I hope I keep you interested in it to actually watch it.

Thank you for your help so far.

I refer you back to my #231, 232, 238 and 240.

The data input to the Tx and the data output of the Rx chips are two state signals - logic signals. Being logic signals they have a specification for what voltage range represents a 0 and what voltage range represents a 1. To help you further - the data input and output can be connected to TTL or CMOS logic gates. The currents which flow during a 0 or a 1 between gates are small - mA or lower. This makes them vulnerable to pick up unless care is taken.

Logic gates have rules on how they are to be used. For example inputs should not be left floating and outputs can only sink or source so much current before the voltage goes outside the range for a 0 or 1.

If you connect one electronic circuit to a point in an another electronic circuit operating with small currents you will inevitably have some impact on the operation of either or both circuits - sometimes it will not be noticeable and other times it will to the point of changing one, the other or both circuit's operation. When this happens the signal passing across the interface between the two circuits will not be what you thought it would be. To prevent one circuit disturbing another interfaces have to be carefully studied and often a buffer circuit designed and introduced between them. I mentioned this earlier.

When a mechanical switch or finger as you are using is used to generate a voltage change to represent a 0 or 1 its output is often unsuitable to be directly connected to a logic gate input because of contact bounce.

Finally - for now - data circuitry can be as vulnerable to interference and noise as analogue unless care is taken to have robust voltage levels representing logic states and transitions between states are very quick and without any bouncing between states. The voltages representing a 0 or 1 should not be near the upper threshold for 0 or lower threshold for 1 to avoid interference and noise 'pushing them into the separation band voltage ranges when a 0 or a 1 is undecidable by the logic electronics a situation which will produce random 0s or 1s.

I suggest you use your oscilloscope and examine the nature of the signals you are creating eg: at the data input to the Tx and at the ouput of the Rx. You will then have an image in your mind of their waveform and suitability and what is required to clean them up and make them robust and thence reliable for data transfer without error.

 

[_q12x_]

I refer you back to my #231, 232, 238 and 240.

The data input to the Tx and the data output of the Rx chips are two state signals - logic signals. Being logic signals they have a specification for what voltage range represents a 0 and what voltage range represents a 1. To help you further - the data input and output can be connected to TTL or CMOS logic gates. The currents which flow during a 0 or a 1 between gates are small - mA or lower. This makes them vulnerable to pick up unless care is taken.

Logic gates have rules on how they are to be used. For example inputs should not be left floating and outputs can only sink or source so much current before the voltage goes outside the range for a 0 or 1.

If you connect one electronic circuit to a point in an another electronic circuit operating with small currents you will inevitably have some impact on the operation of either or both circuits - sometimes it will not be noticeable and other times it will to the point of changing one, the other or both circuit's operation. When this happens the signal passing across the interface between the two circuits will not be what you thought it would be. To prevent one circuit disturbing another interfaces have to be carefully studied and often a buffer circuit designed and introduced between them. I mentioned this earlier.

When a mechanical switch or finger as you are using is used to generate a voltage change to represent a 0 or 1 its output is often unsuitable to be directly connected to a logic gate input because of contact bounce.

Finally - for now - data circuitry can be as vulnerable to interference and noise as analogue unless care is taken to have robust voltage levels representing logic states and transitions between states are very quick and without any bouncing between states. The voltages representing a 0 or 1 should not be near the upper threshold for 0 or lower threshold for 1 to avoid interference and noise 'pushing them into the separation band voltage ranges when a 0 or a 1 is undecidable by the logic electronics a situation which will produce random 0s or 1s.

I suggest you use your oscilloscope and examine the nature of the signals you are creating eg: at the data input to the Tx and at the ouput of the Rx. You will then have an image in your mind of their waveform and suitability and what is required to clean them up and make them robust and thence reliable for data transfer without error

Very good explanation and solution making ! I am exactly at this stage right now, modifying the output Rx with a new circuit (like a buffer) to drive normally the wing leds. Big problems so far, but I will take care of them, 1by1. Hopefully. Thank you for your very nice discussion here. Much appreciated.

 

[_q12x_]

today i build the oscilator for the Transmitter Tx.

 

[marconi]

I will be interested to hear about your progress.


I have had a break from my version. Here in the UK we have the 6 Nations Rugby competition this weekend ( - a deserved victory to Wales against England yesterday) the weather has been so good I have spent time outside instead of in my shed.

I have been thinking (mulling) over whether to experiment with a 940nm array next or to pulse at 10kHz (say) my current 850nm arrays four leds and filter the IR photodiodes output of ambient background and active illumination. So, I have been doodling with circuitry for the pulsed approach next.

I hope you are well and happy.

Best wishes

Marconi

 

[_q12x_]

Another failure but it teaches me something important! Dont mess with the interferences because they will mess you up !!! I got messed up by interferences so I quit it, this was the conclusion after all the experimentation with the RF boards.
All this experimentation I did with a very good friend from america , and very patient, whom we were talking live through an audio live conference and he guided my --- to do all the experimentation needed, but it failed because I have too much interference in my area where I live. ANd i trust him very much because i can't find any other explanations for the weirdness I got, especially after mounting a long wire antena.
I am back to the alternative, or plan B of the remote, using IR, and now for good.
We will try to make a Tx and Rx for the IR remote. It will involve an opamp (uA741) that I only have.
My request from you, is simple. Do you know how to make such a Tx and Rx?
I never in my life built such things. THis is my first time. And is having its up's and down's but this is experience and I like it.
I will start thinking to something myself.
My friend will come back to me after 2 days from now. Because he is having some stuff to make as well.
I am summoning you , mister @marconi to make it in these 2 days.
So only the schematic you have to make.
THe hard part is for me, to actually test it. I'll search on the internet for free circuits for IR remotes and see what I can built by my own.
What an experience with the RF. Phhh.

These are the IR leds and receivers I have, it it helps : https://www.ebay.com/itm/100pcs-3mm-850nm-LEDs-infrared-emitter-and-IR-receiver-diode-50pairs-diodes/323206187341?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

 

[marconi]

I have just watched your latest video. I gather that you have achieved a Tx which will send short pulses of RF to the Rx. The data signal into the Tx pin looks satisfactory. Could you produce a short video for me showing the signal on your 'scope at the Rx data pin and at pin 3 of the Rx's 555 chip please?

I think you may be giving up on RF too soon. If you wish I will spend some time with you trying to iron out the problems. But first I would like to see the signals at the Rx end.

Please let me know if you wish me to help with the RF remote control. If you do could you also draw the circuitry for me at the Tx and Rx?

 

[marconi]

I have studied your last video carefully and if my eye-sight does not deceive me you are using the 555 as a 'sawtooth' voltage waveform generator at pin 2 - the purple one in my attached diagram. There is too a square wave output of the same period from pin 3 - the yellow waveform.

The 555 is kept in the reset state - outputs pin 2 and pin 3 - at 0V when the reset pin 4 is kept at 0V. Upon receipt of a series of data pulses 0-5-0-5-0....V from the Rx data pin, the diode-capacitor network will charge up until pin 4 crosses the threshold to become active high. Then the 555 is no longer ins reset state and oscillations at pin 3 and 2 begin. When the data pulses stop, the capacitor discharges until pin 4 becomes active low and the 555 is once again in the reset state and oscillations stop.

Pressing the button on the remote will then produce a repetitive pulsed output with almost 99% mark to 1% space ratio and a sawtooth waveform of the same period until the remote button is released.

The circuit is not quite correct for interface to your LM3915 pin 5. What you want to happen is a voltage to be input to its pin 5 which is 0V when the remote is not in use. When the button is pressed the pin 5 voltage must grow from 0 to 5V and remain at 5V until the button is released. Upon release of the button the voltage reduces to zero again. See my second diagram.

We can fix this.

 

[marconi]

https://www.electronics-tutorials.ws/waveforms/555_timer.html

At the Rx rewire the 555 to be a negative pulse triggered mono stable timer. An example is shown in the link above.

At the moment the output of the Rx when fed in to the diode resistor capacitor network produces a positive going pulse ie on button press it goes 0 to 5V when the remote control button is pressed. You need to invert this signal so that it is a negative going pulse ie 5 to 0V.

If you insert an npn transistor in common emitter mode between the output of the diode capacitor resistor network and pin 2 of the 555 this will be achieved. The collector load is say a 10k resistor. To limit the base to emitter current put say a 10k resistor in series with the lead from the capacitor to the base. Pin 2 is connected to the collector. When the transistor is off the collector and pin 2 will be pulled up to 5V. When the transistor turns on it will be pulled down to 0V.

you may need to adjust the resistor and capacitor values so that you obtain a waveform like the red one I drew earlier at the output of the didodecapres network. When you press the remote you want the cap to charge up to 5V and stay at this voltage until the button is releasEd. Check this using you scope. You don.t want to see much ripple.

Ripple Voltage in Rectifiers - Instrumentation Tools - https://instrumentationtools.com/ripple-voltage-rectifiers/

 

[_q12x_]

hello mister @marconi and good evening.
Thank you for your help! Can you possibly join me on skype for a momment? I have some stuff i cant put online. And also we can verbally communicate. Here is my id on skype: totoq12 and I have the same robot face there as here on this website, very easy to recognize me.

 

[_q12x_]

Thank you for joining me, listening , advising and helping ! You are a very good friend.

 

[marconi]

A quick sketch of what we discussed. As a first step make this 555 circuit but leave it disconnected from pin 5 of LM3914. Connect your scope to pin3 and observe what waveform is produced and then observe the waveform across C2 each time you operate the remote push button. You may need to adjust R3 and C3 to minimise ripple. The on period ie t1 is determined by R1 and C1.

 

[marconi]

The idea behind this Rx end monostable circuit is that it causes your wings to illuminate inwards to outwards and then extinguish outwards to inwards after only one short duration press of the remote control button. There is no need to hold the remote button down for long. All the remote control is doing is triggering the monostable into action.

 

[marconi]

Small formula error for t2 corrected in attachment below.

 

[_q12x_]

ok, I copied the circuit on my piece of paper right now and I notice there is no value for any components, except that 10K in the collector.
Can you be so kind and put there some values for those components please?

 

[_q12x_]

I just google around and I remember you told me some values are from the other circuit, and I put these values. This is looking good so far?

 

[marconi]

I have just constructed the 555 Rx monostable circuit and connected to my first prototype in which the column of 8 yellow leds represents the leds of your wings. This circuit is on the right in the video and the right hand red led indicates the received and elongated pulse from the Tx.

On the left hand side is a 555 astable which produces a pulse output at a frequency of about 5-10Hz. It represents the output from the data pin of the Rex when the Tx button is pressed briefly. You can see its red led flicker on and off when I press and the release briefly a push button which turns this circuit on and off. The pulsed output is fed into the diode-resistor-capacitor circuit you have already constructed. The voltage across the capacitor connects to the base of the npn transistor which switches pin 2 of the Rx 555 between 5 - 0 -5 V to produce the negative going trigger pulse to initiate a monostable cycle.
Pin 3 of the Rx 555 is fed to a series CR circuit. The voltage across the Capacitor is Vs which feeds into the comparators which drive the 8 leds.

It works then at least on my bench.

?
ps I could not read R4 in the video So I used 10k. I see in your last post you used 47k. I will do the same.

 

[marconi]

R2 and C1 will make t1 about 1 second. You may wish to make this time constant longer. For the testing phase it is rather too short to check operation. I suggest you increase R2 or C1 by a factor of 5 so the pulse output from the monostable is about 5 seconds.

t2 determined by R3 and C3 is a time constant of about 220 x 10exp-6 seconds which is very short. If t1 is about 5 seconds you want t2 to be about 2 to 3 seconds. Easiest thing is to increase R3 or C3. A bit of trial and error until you have a t1 you are happy with and t2 < t1. Assume t2 = R3 x C3 seconds and then adjust until you have achieved t2 < t1.

The idea is for a brief burst of pulses from the Tx to trigger the Rx monostable. This way you conserve the life of the batteries in the Tx.

 

[marconi]

Do ask if there is anything you do not understand. For me, your project is more about an opportunity for me to help you to learn more about the art of electronics.

 

[marconi]

My component values shown in green in the attachment.

I will work on a circuit to combine the rf and proximity signals for input to pin 5 of lm3914.

 

[_q12x_]

Sorry for not responding straight away. My bad. But I was already in a parallel project. I started it in the night before talking with you. I interrupted it while talking to you, and then I got back to it immediate after that.
It was a necessity project. I had that problem when you have only 1 good power supply but 2 tools to be powered from it. So I made this board that is powering them both, from 1 power supply. Pretty neat, right? Again, necessity is the mother of inventions !
Here is a movie with it, a bit long(13min) :

I will get back to the project I discussed with you in a very short while.

 

[marconi]

I have been re-reading the datasheet on the LM3914 because I have been wondering whether it and its associated circuitry is oscillating and being unstable - dependent on the number of LEDs illuminated - worse when several LEDs are on or all are on. Do you think it is oscillating or shimmering or the first LED is slow to illuminate?

I wonder whether the 0V rail has a low enough resistance back to the power supply and whether the 0V and 5V supply to the LM3914 at pins 2 and 3 respectively is not decreasing too much as the LED light. You could do some checks on this with your voltmeter and scope.

Also, it is important for all 0V lines for the LM3914 and to items it connects to are all brought together to one point very close to terminal 2 - see Figure 1.

If it was me I would make up some thicker wire jumper leads with crocodile clips andusing these to parallel the 0V run from the PSU to pin 2 to see if it improved matters. And then repeat with another set taking 5V to pin 3.

Is there any disturbance to the illumination of the LEDs when the relays open or close?

https://www.ti.com/lit/ds/symlink/lm3914.pdf?ts=1614700327590&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FLM3914

Page 18 'Application Hints'-

Three of the most commonly needed precautions for using the LM3914 are shown in the first typical application drawing showing a 0V–5V bar graph meter. The most difficult problem occurs when large LED currents are being drawn, especially in bar graph mode. These currents flowing out of the ground pin cause voltage drops in external wiring, and thus errors and oscillations. Bringing the return wires from signal sources, reference ground and bottom of the resistor string (as illustrated) to a single point very near pin 2 is the best solution. Long wires from VLED to LED anode common can cause oscillations. Depending on the severity of the problem 0.05μF to 2.2μF decoupling capacitors from LED anode common to pin 2 will damp the circuit. If LED anode line wiring is inaccessible, often similar decoupling from pin 1 to pin 2 will be sufficient.

If LED turn ON seems slow (bar mode) or several LEDs light (dot mode), oscillation or excessive noise is usually the problem. In cases where proper wiring and bypassing fail to stop oscillations, V + voltage at pin 3 is usually below suggested limits.

 

[_q12x_]

Thank you mister @marconi. Very interesting what you find ! I must confess, that I did read this pdf a tiny bit. I should give it a full read as you just did now. But the problem is a bit more complicated than this, because alone, unlinked to the RF receiver, does not fluctuate or misbehave. ONLY when is linked (pin5) to the output of the RF receiver circuit after the 555 oscilator, ONLY then, it starts oscilating and random patterns in different times when I freshly connect it. So, it is very stable by it's own, but that particular circuit, with that 555 in it, it just messing it up. I will have to make a movie, showing this erroneous behaviour and explaining what I did ... hopefully as complete as I can and if I even remember all the permutations I did. At least the major ones.
There is an exception. When the 555 circuit is not added to the Rx on the receiver, and pin5 is connected directly to this Rx, all is doing fine, not oscilating, but not working as desired as well. I didnt try your circuit yet since I had to do that other projekt, but I will very soon and I will announce you how it went. Im a bit demoralized by these attempts, but I will get over them.